5 files changed, 96 insertions, 7 deletions

diff --git a/internal/check.go b/internal/check.go
index 8a554ee..a9efd29 100644
--- a/internal/check.go
+++ b/internal/check.go
@@ -8,8 +8,9 @@ import (
 )
 
 type check struct {
-	Plugin string
-	Args   []string
+	Plugin    string
+	Args      []string
+	DependsOn []string `json:"DependsOn,omitempty"`
 }
 
 type namedCheck struct {
@@ -43,6 +44,14 @@ func (c check) run(ctx context.Context, name string) checkResult {
 	return checkResult{name, output, nagiosCode(cmd.ProcessState.ExitCode())}
 }
 
+func (c check) skip(name, output string) checkResult {
+	return checkResult{name, output, unknown}
+}
+
 func (c namedCheck) run(ctx context.Context) checkResult {
 	return c.check.run(ctx, c.name)
 }
+
+func (c namedCheck) skip(output string) checkResult {
+	return c.check.skip(c.name, output)
+}
diff --git a/internal/config.go b/internal/config.go
index 85782cf..cb55ec8 100644
--- a/internal/config.go
+++ b/internal/config.go
@@ -53,3 +53,14 @@ func newConfig(configFile string) (config, error) {
 
 	return config, nil
 }
+
+func (c config) sanityCheck() error {
+	for name, check := range c.Checks {
+		for _, depName := range check.DependsOn {
+			if _, ok := c.Checks[depName]; !ok {
+				return fmt.Errorf("check '%s' depends on non existant check '%s'", depName, name)
+			}
+		}
+	}
+	return nil
+}
diff --git a/internal/dependency.go b/internal/dependency.go
new file mode 100644
index 0000000..020b4f5
--- /dev/null
+++ b/internal/dependency.go
@@ -0,0 +1,51 @@
+package internal
+
+import (
+	"context"
+	"fmt"
+)
+
+type dependency struct {
+	okMap  map[string]chan struct{}
+	nokMap map[string]chan struct{}
+}
+
+func newDependency(config config) dependency {
+	d := dependency{
+		okMap:  make(map[string]chan struct{}, len(config.Checks)),
+		nokMap: make(map[string]chan struct{}, len(config.Checks)),
+	}
+
+	for name := range config.Checks {
+		d.okMap[name] = make(chan struct{})
+		d.nokMap[name] = make(chan struct{})
+	}
+
+	return d
+}
+
+func (d dependency) ok(name string) {
+	close(d.okMap[name])
+}
+
+func (d dependency) notOk(name string) {
+	close(d.nokMap[name])
+}
+
+// Wait for all dependant checks to be executed!
+func (d dependency) wait(ctx context.Context, dependencies []string) error {
+	for _, dep := range dependencies {
+		if _, ok := d.okMap[dep]; !ok {
+			// We sent an error mail already via config.sanityCheck for this case.
+			continue
+		}
+		select {
+		case <-d.okMap[dep]:
+		case <-d.nokMap[dep]:
+			return fmt.Errorf("dependency '%s' is not OK!", dep)
+		case <-ctx.Done():
+			return fmt.Errorf("waited for too long for dependency '%s': %s", dep, ctx.Err().Error())
+		}
+	}
+	return nil
+}
diff --git a/internal/run.go b/internal/run.go
index 2fd1f7c..9583a69 100644
--- a/internal/run.go
+++ b/internal/run.go
@@ -8,6 +8,10 @@ func Run(ctx context.Context, configFile string, renotify bool) {
 		panic(err)
 	}
 
+	if err := config.sanityCheck(); err != nil {
+		notifyError(config, err)
+	}
+
 	state, err := readState(config)
 	if err != nil {
 		notifyError(config, err)
diff --git a/internal/runchecks.go b/internal/runchecks.go
index 360a1b5..48a80e8 100644
--- a/internal/runchecks.go
+++ b/internal/runchecks.go
@@ -11,6 +11,7 @@ func runChecks(globalCtx context.Context, state state, config config) state {
 	limiterCh := make(chan struct{}, config.CheckConcurrency)
 	inputCh := make(chan namedCheck)
 	outputCh := make(chan checkResult)
+	deps := newDependency(config)
 
 	go func() {
 		for name, check := range config.Checks {
@@ -34,17 +35,30 @@ func runChecks(globalCtx context.Context, state state, config config) state {
 
 	for check := range inputCh {
 		go func(check namedCheck) {
+			defer inputWg.Done()
+
+			if err := deps.wait(globalCtx, check.DependsOn); err != nil {
+				deps.notOk(check.name)
+				outputCh <- check.skip(err.Error())
+				return
+			}
+
 			limiterCh <- struct{}{}
-			defer func() {
-				<-limiterCh
-				inputWg.Done()
-			}()
+			defer func() { <-limiterCh }()
 
 			ctx, cancel := context.WithTimeout(globalCtx,
 				time.Duration(config.CheckTimeoutS)*time.Second)
 			defer cancel()
 
-			outputCh <- check.run(ctx)
+			checkResult := check.run(ctx)
+
+			if checkResult.status == critical {
+				deps.notOk(check.name)
+			} else {
+				deps.ok(check.name)
+			}
+
+			outputCh <- checkResult
 		}(check)
 	}